Do not delete bootstrap.exe on Windows during clean

[rylev]

Windows does not allow deleting currently running executables.

This an addition to @jyn514's change in #80574.

[rust-highfive]

r? @Mark-Simulacrum

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[the8472]

I thought windows 10 introduced a way to use posix unlink semantics, can't we use that?

[rylev]

@the8472 I believe we could theoretically use _unlink on Windows 10, but this doesn't work on older versions of Windows which is why the std library doesn't use it. Do we want to limit bootstrapping to Windows 10?

[the8472]

I mean we could avoid skipping cleanup if the system supports unlink semantics.

[Mark-Simulacrum]

I don't think platform version specific logic is worth it, personally, but I would like for us to warn the user when we fail to fully clean - it might also make sense to still try to clean up most of the bootstrap directory, even if we can't quite get the bootstrap binary.

[rylev]

@Mark-Simulacrum I've added more handling so the user is informed when something goes wrong on Windows.

[ChrisDenton]

I thought windows 10 introduced a way to use posix unlink semantics, can't we use that?

Not for running binaries, IIRC. Even with posix unlink semantics (which is now the default for DeleteFileW), Windows honours exclusive file locks. And last I checked the exe loader still loads the binary without the FILE_SHARE_DELETE permission so nobody else can delete it.

There's no harm in trying though.

[jyn514]

Rustup has had serious problems with this (cc @kinnison), so if you figure out a way please let them know. I'm inclined to think it's not worth messing with, though.

[ehuss]

There's no harm in trying though.

I tried a quick test with _unlink, and it still fails if the executable is running. I'm pretty sure it is not possible.

[ChrisDenton]

Yes, that it's not currently possible was the message I was trying to convey with my explanation. Obviously I worded that badly, sorry. To rephrase: The Windows executable loader (which is outside Rust's control) does not currently set FILE_SHARE_DELETE which makes the .exe impossible to delete.

My point in that last sentence was only that there is not a problem with attempting to delete and handling the expected failure. The worst case it fails gracefully, which can be handled, and in the best case some future version of Windows allows deleting running applications.

[Mark-Simulacrum]

@bors r+

[bors]

📌 Commit 5b0ed02 has been approved by Mark-Simulacrum